Manufacture of insulated electric conductors



Nov. 8, 1955 .J. A. MGCLEERY 2,722,963

MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS Filed Aug. 25, 1954 Inventor r/mes l/eranaer AFC/rely fi torney United States Patent ,9 P

MANUFACTURE OF INSULATED ELECTRIC CONDUCTORS James Alexander McCleery, Sale, England, assignor to British Insulated Callenders Cables Limited, London, England, a British company Application August 25, 1954, Serial No. 452,106

Claims priority, application Great Britain September 10, 1953 4 Claims. (Cl. 1542.25)

This invention relates to electric conductors consisting of a wire or wires in a tube of metal insulated by powder, for instance magnesia or talc, the powder being compressed by a tamping method as it is fed into the tube around the wires. A usual method of manufacturing such insulating conductors is to make the assembly with the parts of comparatively large size and then to reduce the diameter and extend the length by a drawing process.

The invention is concerned with the removal of air from the interior of the tube and its replacement by another gas which may be inert or protective, or have other useful properties. In accordance with the invention an assembly is made of the tube containing the conductor, or conductors, closed at one end by a plug and suitably enclosed at the other end for the filling in of the powder; this assembly is then exhausted of air by connection to suitable vacuum apparatus and thereafter is charged with the other gas under pressure. A container enclosing powder to serve as a supply for filling the tube is also exhausted of air and charged with the gas. This is preferably done as a separate operation, the tube assembly and the container being only put in communication after the charging with gas of each one of them has been completed. The powder is then caused to flow from the container into the tube assembly and filling and tamping proceed until the operation is complete. This operation is, accordingly, carried out in an atmosphere of the selected gas and the spaces Within the mass of compacted powder remain filled with this gas. It is preferred to leave a sup ply of gas under pressure in communication with the apparatus during the filling operation so as to maintain the pressure in spite of any leakage which may occur.

The arrangement of apparatus which we prefer to use isone in which a tamping ram reciprocates in the tube while the powder is fed into the space between and below the ram, using the known type of tamping device in which the reciprocating ram is driven through a yielding frictioncoupling so that the ram may rise up within the tube as the filling proceeds. This arrangement facilitates the enclosure of the tube assembly and its connection to the powder container and the gas supply.

The invention will be described further with the aid of the accompany-ing drawings wherein:

Figure 1 illustrates in elevation and diagrammatically one form of apparatus suitable for carrying out the invention and Figure 2 is a fragmentary View in elevation shown partly in section.

The reference numeral 1 indicates a vertically disposed metal tube and the reference numeral 2, a conductor which is disposed centrally of the tube and is insulated therefrom by an insulating powder 3. The outer tube, for example, may be of copper and the conductor have the form of a copper rod. The powder is fed continuously into the upper end of the tube 1 from a container 4 through a pipe 5, the powder being discharged from the latter into the upper end of a funnel 6 attached to the upper end of the tube 1.

2,722,963 Patented Nov. 8, 1955 ICC As the powder 3 is fed into the tube 1, it falls down the tube where it is tamped around the conductor 2 by a ram indicated generally by the reference numeral 7. The ram has a longitudinally extending passage so that it may pass over the conductor while being reciprocated within the tube 1. The ram has at its lower end a head 8 and a ram rod 9 projecting upwardly therefrom. The head of the ram is constructed in such a manner that the powder 3 can fall past it and be compressed by the head 8 as the ram is reciprocated. The upper end of the ram rod 9 is connected to a piston 11 working in a cylinder 12, by a piston rod 13, which is connected to the ram rod 9 by a sleeve 14 which engages the ram rod frictionally, permitting relative movement to take place between the sleeve and the ram rod when the head 8 of the ram is brought into contact with the powder 3 beneath it. As the feed of the insulating powder is continued, the head of the ram gradually rises up the tube 1. The friction between the sleeve 14 and the ram rod 9 is sutficient to obtain effective tamping of the powder round the conductor 2. The cylinder 12 is fitted with pipes 15 and 16 for the. admission of compressed air or other fluid to opposite sides of the piston 11 to cause the latter to reciprocate within the cylinder.

After the tube 1 has been filled with the insulating powder 3, the tube and its contents are drawn through a die to produce elongation of the conductor 2 and a reduction in diameter of the tube with elongation of the latter. This results in an insulated conductor in which the insulating powder is well compacted round the conductor and the tube tightly fitting over the insulated conductor, the assembly being of comparatively small diameter and the insulated conductor of the required length. Normally, this final product will contain air at atmospheric pressure. It is an advantage that the final product should contain some other gas at a pressure above atmospheric. The apparatus illustrated permits this result to be obtained.

Referring to Figure l, a. vacuum pump 17 is connected to one side of a filter 18 by a pipe 19. A pipe 20 provided with a valve 21 is connected to the other side of the filter and to a pipe 22. To the latter is also connected a pipe 23 and to the latter is connected one end of a pipe 24' having a valve 25. The other end of the pipe 24 is connected to a short pipe 26 connected to the upper end of the pipe 5 and to the lower end of the container 4. The pipe 26 has a valve 27. The upper end of the funnel has a cap 28 which makes a gas-tight fit with it and is provided with a gland 29 which permits the ram rod 9 to slide through it in a gas-tight manner. The lower end of the tube 1 is fitted with a gland or plug 30 which makes a substantially gas-tight fit with the conductor 2, the latter passing through the gland 30 for a short distance. The tunnel 6 is connected in a gas-tight manner with the upper end of the tube 1 by a gland 31. Communication can thus be established between the vacuum pump 17 and the tube 1.

A cylinder 32 containing a gas, other than air, under pressure, for example, nitrogen, is connected to the pipe 22 through a pipe 33 connected to the cylinder and to a pipe 34 provided with a valve 35, pipe 34 being connected to pipe 22. Communication can thus be established between the cylinder 32 and the tube 1.

The apparatus also includes means for exhausting the container 4 and charging it with the gas under pressure in the cylinder 32. The pipe 23 is connected to a pipe 36 provided with a valve 37, the pipe 36 being connected in a gas-tight manner to the upper end of the container 4. The evacuation and charging of the tube 1 and the evacuation and charging of the container 4, preferably, are carried out as separate operations, the container and the tube 1 being placed in communication with each other when both contain the gas under pressure. This communication is established by opening the valve 27 in the pipe 26. The container 4 is filled with an appropriate quantity of powder before being evacuated and charged with gas. This quantity of powder, preferably, is sufiicient to filll several of the tubes 1.

If the tube 1 is to be evacuated and charged with gas before the container 4, evacuation of the tube is efiected by opening valves 21 and 25, valves 35, 37 and 27 being closed. Charging of the tube 1 with gas under the required pressure is effected by closing valve 21 and opening valve 35, valve 25 being open and valves 37 and 27 being closed. Evacuation of the container 4 is effected by opening valves 25 and 37, valves 35 and 27 being closed and valve 21 being opened. Gas under pressure is admitted to the container 4 by closing valve 21, opening valves 35 and 37, valves 25 and 27 being closed. Upon obtaining equal gas pressures in the tube 1 and the container 4, the valve 27 is opened to commence the feeding of the powder from the container into the tube 1 and the reciprocation of the ram 7 within the tube. By equalizing the pressures in the tube and the container, there is little tendency for the gas to leak from the tube 1. Should there be any tendency at the gland or plug 30, the packing of the powder by the ram assists in facilitating the sealing at that end of the tube.

The yielding friction provided between the sleeve 14 and the ram rod 9 facilitates the mounting of the tube assembly and its connection to the container 4 and to the various pipe connections for evacuation and supply of gas.

Although in the construction shown, only a single conductor is disposed within the tube 1, there may be two or more such conductors, the ram rod 9 having a corresponding number of longitudinally extending passages to receive the conductors. These passages are made of sufficient length to enclose the conductors, the upper portion of the ram rod 9 being solid. The pipe 22 is provided with a pressure gauge 38, which can be used for measuring the air pressure in the container 4 and the tube 1 while being exhausted and the gas pressure in those parts during filling with gas. A gauge 39 may be provided to indicate the gas pressure available in the cylinder 32, and a valve 40 in the pipe 22, should it be required to reduce the pressure at any time to atmospheric. This valve will be kept closed when the apparatus is in operation. The container 4 may be filled with powder through a pipe 41 provided with an air-tight cap 42.

During the charging of the tube with the powder it is preferred to maintain the connection between the tube and the source of pressure gas to compensate for any escape of gas from the tube, should there be any.

After the filling of the tube with powder has been completed, the tube and its contents may be drawn through a die to reduce the diameter of the tube and of the conductor and increase their length to provide a cable having one or more conductors insulated with tightly compacted powder containing a desired gas under pressure and a sheath which fits tightly over the powder insulation.

What I claim as my invention is:

1. Apparatus for attachment to the open end of a metal tube closed at its other end and containing a conductor to be insulated from the metal tube by powder, the said apparatus comprising a container for the powder, a dclivery vessel for sealed attachment to the open end of the tube, a pipe connecting the powder container and the delivery vessel, a gland, a ram rod extending through the gland into the delivery vessel and having a longitudinally extending passage closed at one end and open at the other, means for reciprocating the ram rod, a valve in the pipe between the container and the delivery vessel, means for removing air from the powder container and from the metal tube and for filling the container and tube with some other gas under pressure.

2. Apparatus for attachment to the open end of a metal tube closed at its other end and containing a conductor to be insulated from the metal tube by powder, the said apparatus comprising a container for the powder, a delivery vessel for sealed attachment to the open end of the tube, a powder delivery pipe connecting the powder container and the delivery vessel, a valve in said powder delivery pipe, a gland at the upper part of the delivery vessel, a ram rod extending through the gland into the delivery vessel and having a longitudinally extending passage therein open at its lower end and closed at its upper end, means for reciprocating the ram rod, a source of gas under pressure, other than air, a pipe connecting said source to the powder container at the upper part thereof, a valve in said pipe, air evacuating means connected to the upper part of the container, a pipe connected to the powder delivery pipe on the delivery vessel side of the valve in the powder delivery pipe, said pipe being connected to the source of gas pressure and air evacuating means, and valves for shutting off said source and air evacuating means from said pipe.

3. In a method of manufacturing an electric conductor comprising one or more wires insulated by powder enclosed in a metal tube, the steps which comprise assembling a conductor in a metal tube, sealing the latter and removing the air therefrom and from a confined volume of insulating powder, charging the metal tube and the confined volume of powder with a gas under pressure, other than air, and thereafter charging the tube with the powder and tamping the latter around the conductor.

4. In a method of manufacturing an electric conductor comprising one or more wires insulated by powder enclosed in a metal tube, the steps which comprise assembling a conductor in a metal tube, sealing the latter and removing the air therefrom and from a confined volume of insulating powder, charging the metal tube and the confined volume of insulating powder with a gas under pressure, other than air, the removal of the air and the charging of the confined volume of insulating powder with gas under pressure being carried out as operations which are independent of the removal of the air from and charging of the metal tube with gas under pressure, the metal tube being thereafter charged with the insulating powder and the latter tamped around the conductor.

References Cited in the file of this patent UNITED STATES PATENTS 1,765,804 Preston June 24, 1930 2,477,273 Tognola July 26, 1949 2,680,086 Hollingsworth June 1, 1954 

